An improved external power supply for left ventricular assist devices and total artificial hearts is proposed. The presently used rechargeable battery packs are heavy and require frequent recharging. Since the cardiac patients who use these devices must carry the power supplies, improved patient mobility and quality of life would be provided by a lightweight instantly refuelable power supply. A lightweight, compact, safe and reliable direct methanol fuel cell would fulfill this need. The Phase I program demonstrated a simplified direct methanol fuel cell based on a novel method for supplying the fuel to the fuel cell. The fuel cell will be further developed in the proposed Phase II program, with improvements in fuel cell performance and weight reduction. A simplified fuel cell system will be developed through system modeling and planned experiments. The program will culminate in fabrication and demonstration of a prototype miniaturized 10 W, 80 Whr power supply.